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Cooking Colophony Down For Color, Low and Slow?


Berl Mendenhall
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There was a time when I was trying to make copal varnish using oxidized turp and experienced that reaction. I used boiling chips to minimize it which indicates its passage of something. Boiling chips are always used if odd mixtures are being heated.  Someone on Tobi also mentioned using a wide mouth container  considerably reduces the effect. fred

 

 Someone on Tobi also mentioned using a wide mouth container  considerably reduces the effect. fred

I'd expect so. Don't want to shoot the stuff out through a rocket nozzle.   (Unless you're making a rocket) :)

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You know you only have to mix NaOh with water at 10M (about 40g for 100ml of water) in a falcon tube to discover what an exothermic reaction is. I had to do it few time, and after 1 min or 2, you can hardly hold the tube in your hand (means temp increases above 50C )

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I thought I would like to show the rosin cooking scenario

 

 

 

post-30816-0-89148200-1400516981_thumb.jpg

 

This is a batch of varnish cooked with a portion of rosin from the batch I am cooking right now.

 

Took some out half way through the cooking process, and shows a slapped on thick coat of varnish over a Plaster ground "alla Roger". I wanted a batch of varnish slightly less coloured that the finished one, to make a "girly" viola. 

 

This particular batch is going to be cooked to "Venetian" dark once is ready.

 

Bring on the fumes.

 

 

 

 

 

 

 

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As an industrial chemist who has worked with rosin and related materials for a lifetime, I think some of you are being too cavalier about the hazards of cooking over a flame.  The fire and burn hazards are obvious, but the health risks of exposure to the vapors should not be ignored.  Rosin is a strong allergen and though you may not react to it now, continued exposure can sensitize you (and your neighbors).  People have strong and sometimes life threatening reactions to rosin vapors.  In the US, OSHA has set monitoring and exposure standards for the electronics industry where rosin is used as a solder flux.

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I thought I would like to show the rosin cooking scenario

 

 

 

attachicon.gifIMG-20140519-WA0011.jpg

 

This is a batch of varnish cooked with a portion of rosin from the batch I am cooking right now.

 

Took some out half way through the cooking process, and shows a slapped on thick coat of varnish over a Plaster ground "alla Roger". I wanted a batch of varnish slightly less coloured that the finished one, to make a "girly" viola. 

 

This particular batch is going to be cooked to "Venetian" dark once is ready.

 

Bring on the fumes.

 

Hola José

 

Very nice hue.
Also I am following Roger´s way. Plaster of Paris and his "colofonia varnish".
How much days did you cook the resin to achieve this hue?
 
Regards
Tango
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As an industrial chemist who has worked with rosin and related materials for a lifetime, I think some of you are being too cavalier about the hazards of cooking over a flame.  The fire and burn hazards are obvious, but the health risks of exposure to the vapors should not be ignored.  Rosin is a strong allergen and though you may not react to it now, continued exposure can sensitize you (and your neighbors).  People have strong and sometimes life threatening reactions to rosin vapors.  In the US, OSHA has set monitoring and exposure standards for the electronics industry where rosin is used as a solder flux.

No open flames here, it is a electric hob and the pot is in a sand bath, should be pretty safe. Also, the temperature is so low that it barely fumes out, and even then, the thing is placed by the window. Draft takes all the stuff outside. Neighbour upstairs swears she can't even smell the thing. 

 

 

Tango, I couldn't tell you how many days, so far it must have been around 100 hours. Gonna keep cooking the other half of the rosin another 100 hours. "TO DEATH and BEYOND". 

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I haven't followed this thread but was wondering how the rosin cooking is going for everyone. I am interested in trying the crockpot method. Has anyone had luck with that? Photo's?...

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[ThatH ischment=34137:1401465515395.jpg]

Here's some spruce resins I have cooked on the crockpot.

The one on the right was cooked at 300f about 30 hrs.I stopped since it was not getting much darker than 20 hrs prior and it is not soluble in turps.

On the left was cooked 10 hrs at 420f and is a bit greener, but is soluble in turps. It behaves similar to bass rosin n meaning that it flows some when cold. I'm not sure if that is desirable.

My crockpot will heat to 420f, it takes 3 hrs to get there if I wrap the sides with some insulation. Down side is that it isn't meant to go there, the switch stuck in position.

post-5144-0-81903900-1401465744_thumb.jpg

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Interesting Don. Thanks. What species of spruce resin did you use? Was it the oleoresin from the Norway spruce? Sounds like the crock pot is the way to go. How much resin did you cook at a time in grams?

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I aim to find out what type spruce it is. I collect it in Maine along the coast areas near Brunswick and Portland.

The crockpot works okay but I'm hesitant to leave it on 24/7 since I'm in a residential area. Maybe I need to find an enclosure I can put it in?

I have not weighed anything. I start with a gallon ziplock bag of bark and resin and dissolve about (16 oz ) peanut butter jar about 7/8 ths full of raw resin. That cooks down to about half a jar or a cup or so of cooked resin.

I get a nice color from it but still not dark enough. The samples on the rib stock look good but it is way too thick of a film there.

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Okay so you are collecting it from off the outside of the tree...Have you made a varnish with it yet. How does it dry? I tried making varnish from the Albies Alba resin that I bought from Kremer which is collected in the same manner and made several batches with it by itself and mixed 50/50 with colophony and it simply would not dry. I figured since it was from the same tree that Strassbourg turpentine is collected from it would be the same thing. Wrong, this stuff doesn't dry and softens when the temp gets to high.

I recently talked with Dale from Woodfinishing and he sells Spruce gum. He guaranteed it was from the Norway spruce. However when I inquired about the burgundy resin he contacted his supplier and they could not say what tree it was collected from. Only that the burgundy resin he has is not from the Norway spruce. Same deal with Kremer. Well Thank you for the information.

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I have made a varnish, not from this cook, but from a previous batch of the same resin. It dried very well in a lean mix with linseed oil (approx. 4/1 washed raw oil). It was too chippy though, not sure what to add to make it stick better. I don't want it too tough though.

I suppose it matters most that you have a steady supply of the resin that works, I see your point of wanting to know what suppliers are selling you. They seem happy to call it 'whatever'!

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Here are the two types of colophony I bought recently from Wood Finishing Enterprises:

 

post-43707-0-76612000-1401561242_thumb.jpg

 

Darker is FF grade rosin.  Lighter is "Gum Rosin" WW grade.  

 

I've read other posts stating making a colophony varnish using only the FF grade came out too dark and that perhaps a mixture of the two rosins was a good solution..  

 

Here we are talking about getting some degree of darker color by extended low temp cooking to speed oxidation.  So is the starting point of this process that most of you talking about with lighter rosins, like the gum rosin shown here?  I would assume starting with the draker rosin would be preferable.  And in this cooking, is any umber being used to help along the coloring process?  Or is that step saved for when the oil is added to finally make varnish?

 

Based upon Joe R's previous comments in other threads concerning bonding the pigment directly to the oil molecules for transparency, I would think you would want to try preheating the oil to body it and at the same time add the pigment there in hopes to make this kind of pigment bonding take place.  

 

So just trying to get clarification on whether this process is used to eliminate the need for additional pigments or to assist in the reduction of the amount of pigments necessary to achieve the appropriate color density for the finished varnish.  

 

One last question which hasn't really been answered (that I can tell) relating to the character of the varnish:

 

People comment on a varnish being too hard or too soft when finally applied to an instrument.  How much of this depends upon the percentage of oli to rosin in the cook?  Or does it depend more on the cooking process itself?  Fred has mentioned different ratios in previous threads but not what advantages or disadvantages you get with more or less amounts of oil to rosin.  I made my first two batches more or less following Adelle Beardsmore's recipe which is 2 to 1 oil to rosin.  I also followed Fred's advice adding umber to the cook in addition to the aloe.  It seems to produce a nice consistency red-brown varnish which I have used (more or less) on my first few instruments.  I know this is only one approach.  

 

What ratio of oil to rosin do most makers recommend for a colophony varnish and why?

(Sorry...maybe this is a new thread?)

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Hi Joe S-  WW rosin  is distilled from stumps, unlike gum rosin, is generally referred to as wood rosin. I imagine the color is to some degree similar to extended oxidation that happens to gum rosin. Getting color by long oxidation cook that Roger Hargrave uses, or  my sledge hammer method by high heat and coloring metals like umber are pretty much different methods. The metals added are driers that speed up the time for the varnish film to be tack free, and also add color and still maintain transparency. You can pre-body the oil with the metal, or cook all three. But you can't do this if you were making a fossil copal varnish for the oil would become an insoluble gel before the copal had been cracked enough to become soluble in oil. Copal has to be made cracked before adding oil, unlike rosin.

 

Do you want a hard or soft varnish, I don't think anyone can answer this. Durability and hardness is based a lot on the ratio of oil to resin. The more oil  added to any resin will give you a softer varnish of greater durability, therefore a longer life. I don't think Strad and others were interested in durability but the aesthetics of the finish. I've mainly used a ratio of 10 oil to 15 resin, which is a rather a hard  finish. I think a 1:1 is still a firm varnish. fred

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The Naval Stores Rosin Color Scale is independent of the kind of rosin.  Tall oil, gum, and wood rosin are all graded according to the same scale.  Something like "WW" denotes the color.  Nothing else.

 

see http://www.ssco.com.tw/Tintometer/3000series_comparator/AF607ROSIN.pdf

 

It's more common these days to specify the color of rosin and similar resins using the Gardner Color Scale.

 

see http://www.gardco.com/pages/color/liquidcolor_stds.cfm

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Joseph, I think yours or anyone's results are going to be dependent on the type of rosin/colophony/sap you have and how you cook it with the oil. And then of course the type of oil you have and how it has been washed or aged or what not.

One wouldn't think there would be much difference between the kinds of resins and oils but for making varnishes it does.

Come to think of it I don't think anyone in this thread is using exactly the same resins and oils so I have to remind myself that repeatability doesn't carry over from one cook to the next. That makes it hard to respond to your questions, which are good questions, just that they will be specific to your personal process.

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The Naval Stores Rosin Color Scale is independent of the kind of rosin.  Tall oil, gum, and wood rosin are all graded according to the same scale.  Something like "WW" denotes the color.  Nothing else.

 

see http://www.ssco.com.tw/Tintometer/3000series_comparator/AF607ROSIN.pdf

 

It's more common these days to specify the color of rosin and similar resins using the Gardner Color Scale.

 

see http://www.gardco.com/pages/color/liquidcolor_stds.cfm

Nice information. Thanks

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Hi Joe S-  WW rosin  is distilled from stumps, unlike gum rosin, is generally referred to as wood rosin. I imagine the color is to some degree similar to extended oxidation that happens to gum rosin. Getting color by long oxidation cook that Roger Hargrave uses, or  my sledge hammer method by high heat and coloring metals like umber are pretty much different methods. The metals added are driers that speed up the time for the varnish film to be tack free, and also add color and still maintain transparency. You can pre-body the oil with the metal, or cook all three. But you can't do this if you were making a fossil copal varnish for the oil would become an insoluble gel before the copal had been cracked enough to become soluble in oil. Copal has to be made cracked before adding oil, unlike rosin.

 

Do you want a hard or soft varnish, I don't think anyone can answer this. Durability and hardness is based a lot on the ratio of oil to resin. The more oil  added to any resin will give you a softer varnish of greater durability, therefore a longer life. I don't think Strad and others were interested in durability but the aesthetics of the finish. I've mainly used a ratio of 10 oil to 15 resin, which is a rather a hard  finish. I think a 1:1 is still a firm varnish. fred

Thanks for the continuing help understanding this very complex animal, Fred. :)

Aside from adding hardness to the varnish, is the resin the primary contributer to the color. And metals added to the cook react with the resin to produce colors, the oil just serving as a medium for all this stuff to swim around in?

When I added the umber to the oil last time when I tried heating the oil first for an hour or so, I was probably not doing anything useful for the color of the varnish. I assume I could have just heat bodied the oil without the umber and added the umber to the melted resin before combining with the oil.

Do you see any purpose to do a long slow cook with the FF grade dark colophony to give it more color? (I assume you meant the FF grade in your response above.) I wonder if its dark because of oxidation or impurities? If the latter, would it make a transparent varnish? Or would it be more advise able to start with a lighter WW grade rosin, and color it either by added metals, or the long slow cook?

My varnish (Adelle's) was 2:1 oil to resin (opposite to your ratio) and it seems to dry quickly, (8 - 12 hrs in the UV box) and to polish up nicely. Actually I've been polishing the OW Amber varnish.. My varnish is under the top coats.

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Joseph, I think yours or anyone's results are going to be dependent on the type of rosin/colophony/sap you have and how you cook it with the oil. And then of course the type of oil you have and how it has been washed or aged or what not.

One wouldn't think there would be much difference between the kinds of resins and oils but for making varnishes it does.

Come to think of it I don't think anyone in this thread is using exactly the same resins and oils so I have to remind myself that repeatability doesn't carry over from one cook to the next. That makes it hard to respond to your questions, which are good questions, just that they will be specific to your personal process.

Thanks for pointing that out! And so my question about whether the dark colophony would make a good varnish. Is the color from oxidation or impurities, and if the latter, is that a problem? The particular rosin came recommended in an earlier thread. :)

Joe

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Hi Joe- apologize for incorrect classification- I think WW is water white gum rosin,  FF is dark wood rosin.   Referring to the function of the varnish contents, oil makes the film, resin imparts the hardness, and the way I use umber  is as a drier and colorant. If you were adding umber strictly as a drier you would  add something only around 0.02% umber to the amount of oil. Really tiny amount.

I'm surprised you didn't get any color to the oil when cooked with umber. The manganese in umber should have colored the oil gold brown from my experience. To body the oil to near string in an hour I suspect you should be using a temp around 500F Just a guess. With any rosin, the metals in umber will react with acidic factors of rosin, generating color and reducing the acidity. The long  lo temp cook method oxidizes the abietic acid, which darkens the rosin and also adds the color when spread  out in a film. Keep in mind these are different ways to make a rosin  varnish, long lo temp, short cook with metal. The colors in my finish are also caused by the dyes applied to the wood before varnishing.  fred

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